feat: PXE debug boot mode for rescue/diagnostics

New `labctl provision debug <target>` command that PXE boots a machine
into Fedora rescue mode (inst.rescue) for live debugging. Auto-clears
after one boot so next reboot returns to normal.

Adds debug state to BastionState, dispatch routing, API endpoints,
labd command routing, and CLI with rescue workflow guide.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bastion/src/shared/src/index.ts

@@ -5,6 +5,7 @@ export type {
   HardwareInfo,
   InstallConfig,
   InstalledInfo,
+  DebugConfig,
   BastionState,
   BastionConfig,
 } from "./types/index.js";